Trimmer capacitor



Jan'. 19, 1965 l.. T. BARNES TRIMMER CAPACITOR Filed Oct. 12. 1960 2 Sheets-Sheet 1 INVENTOR. z5/@20W r PAPA/5 BY m v Jan. 19, 1965 l.. T. BARNES 3,66,695

TRIMMER CAPACITOR Filed Oct. 12, 196C 2 Sheets-Sheet 2 INVEN TOR. LEA/5.1.1. )w r .PARA/5s' www@ United States Patent Utilice f j TRIMMER CAPACITOR l Llewellyn T. Barnes, 155 Atlantic Ave., "Freeport, N.Y., assigner of one-third to Charles T. Barnes,{Freeport, and one-third to JohnF. Woog, Garden City, N.Y.

Filed Oct. V12, 1960, Ser. No.' 62,295

' 3 Claims. (Cl. 317-249) My invention relates to improvements in variable electrical capacitors and specifically, to capacitors ofthe trimmer type which are used to produce precise capacity variations. v v f Trimmer capacitors of the type exemplified by United States Patent No. 2,607,826 issued to me onl August 19, 1952 include a cylindrical body made of dielectric material. A band of conductive material is sprayed on the outside of this cylinder adjacent .one end thereof and serves as the fixed plate of the capacitor. Thevmovable electrode comprises a piston and a screw ofconductive material formed integrally thereon and threadedA throughout its length and received by a threaded bushing at one end of the cylinder, thus, rotation of the screw will result in rotation and axial movement of thepiston relative -to the fixed band, thereby 4changing the capacity of the unit.

An anti back-lash mounting means is provided in this aforementioned trimmer-,capacitor and includes a nut in threadedr` engagement with the screw, means to prevent the nut from turning as the screw rotates, and a springexertingpressure on the nut to bias the nut into iirm engage-` ment with the screw atall times.

Patented Jan. `19, 1965 f mer-type piston capacitor which is composed of few parts,

vWhil'ethis typeof piston trimmer'provides effective operationit presents the drawbacks'ofrequiring careful machiningof parts, particularly the pistonandscrewsince they are formed integrally and the screwA is threaded vthroughout its length. Furthermore, the ,bushing must be tapped andthreaded' tofreceive the screw, and -means provided in thev ybushing to prevent rotation of thef'afore-y said nut. -These variousmachining operations notlonly incur high production costs but also increase assemblyftirne Ofheunit. i

In accordance with the invention herein, there ispro'- i vided a piston trimmer type capacitor Vhavinga cylindrical 'body of a high dielectric material. An 'adjustingy member, which is/threadcd for only a lsmall'distanceat onere'nd, isl

frictionally mounted in a bushing attached'tojthe cylindrical body. Thethreaded endof the adjustingme'mber is in threaded engagementwith'one endno'f an internally threaded piston. Theother end ofy the piston-is attached' to a ,washer having a'square aperture which coacts with a square projection within the cylinder and thereby prevents 'the piston from rotating. Thus,'rotation of the screw will result in only longitudinal vmotion Iof the piston relative to' Y, and abuts the rear wall of the bushing. rA second washer is mounted onthe notch in the adjusting member and va spring'is compressed between the two washers, therebyV exerting biasing forcel on the second Washer which always keeps theadjusting member under tension,kr 4thus'eliminating backlash.

One of the objects of the invention is to provide a piston type trimmer capacitor of the'character described which requires `a minimum of machining to produce.

,Another objectV of the invention is to provide a simple meansV of eliminating backlash a piston-typetrimmer capacitor of the character described. i f `1 A further object of the invention is to provide a trimis simple to construct and assemble, lends itself tomass production techniques, and at the same time is effective to prevent rotation of the piston.

Additional objects and advantages of the invention will FG. 2 is a central longitudinal section throughthe capacitor of FIG. l; I t FIG. 3 is a transverse section taken along 3-3 of FG. 2; and i FIG. 4 is an exploded perspective view of the capacitorv Referring in detail to the drawings, particularly to FIGS. 2 and 4, there is shown a capacitor 10 made in accordance with the invention and having a front end bushing 11. The bushing 11 is formed with a central aperture 12 communicating with an inner bore orrchamber 13. The bushing 11 also has a chamfered or tapered forward surface 14 adjacent aperture 12 for a reason hereinafter explained. Bushing 11 is also provided with an external circumferential flange 16 from which projects an end annular flange 1S of reduced diameter.

A hollow cylinder' 17, made of a dielectric material such as quartz, glass, Titania or the like, is rigidly and con- Y centrically attached to the bushing 11. A band 24 of a conductive metal such as silver, is fitted about the outer `surface of cylinder `17 adjacent the rear end thereof, and is secured to saidcylinder outer surface, as by cementing.`

As an alternative, the hand mail be sprayed on the cylinder surface land then ired.- v

The annular iiange 15 vof bushingrllisfinserted within s the` front open end' of cylinder 17 andY secured therein as by cementing. with the end of cylinder ,17 abutting flange 16 andchamber 13 communicating with the interior of cylinder 17, as shownY in FIG. 2. i

The capacitor 1t) also includes an adjusting member indicated generally by reference numeral 21 and comprising-v shank portion 26 and which is complementary to the taperedl surface 14 of bushing 11 adjacent aperture'12.

Thus, adjusting member 21 in assembly can be inserted through aperture 12 ofbushingl 11.until the .tapering portion 4@ of head piece 23 is seated upon the tapered surface 14 of said bushing 11. Y v

The kconductive bandA 24 constitutes aiixed electrode of the condenser 10 exteriorly of the dielectric wallvof cyl inder 17. The condenser 10 also includes a movable elec-V frode designated generally by reference'numeral 18 on the inner surface of cylinder 17. Electrode 13 is slidable in cylinder 17 and comprises a vcylindrical metal piston 19 having a central threaded bore 41, and a washer 2li, made of non-conductive material, cemented to one end of piston 19. Washer 2i) is provided with a square central aperture 20a which is in alignment with the threaded bore '41 of piston 19. The bore 41 isin threaded engagement with threaded portion 22 of adjusting member 21. l

The cylinder 17 is closed'of by an end cap 32 which is j force-fitted within the rear open end` of cylinder. 17,'and

is provided with an integral inwardly-projecting post 31 of square cross-section. Post 31 is sized to tit' within the square aperture 20d of washer 20. l Thus, while washer 2t) can slide" along post 31, neither Washer 20`r`1or the piston 19 carried 'thereby can rotate relative to post 31 or 'cylinder17.v 'i

rotated thereon.

I seat.

` resilient to permit the washer to be deformed and stretched arcanes Electrode 18 therefore is constrained to move longitudinally through cylinder 17 without rotation therein. They Shanky 39 of adjusting member 21is formed with a notch 27 which is sized to rictionally receive and retain a horseshoeshaped washer 393, as shown inFIGS. 2 and 3. The Washer 33 has ,an annular recess or groove 34 cut in its outer face and serving asa spring seat, as willbe presently described. A circular washer 28 made' of insulating material such as nylon, contains a square aperture 43 which lits about the square shank portion 26 so that While the insulated washer 28 may be slidv longitudinally alongsaid square shank portion 26, it cannot be Thewasher 28 has'a recessed annular groove 29 on its inner surface which serves as a spring The body' of washer 28 is suiciently flexible and so that its square aperture 43 may pass over the shank threaded portion 22 when washer 28 is mounted onA adjusting member 21. f

A compression spring 30 is mounted within chamber 13, one end of said spring '30 being seated in the annulargroove 29 ofA washer 28' and the lother end of spring 3) beingseated in groove 34 of washer 33.. The spring 3() thus presses the insulated washer 28 against the end wall of bushing lland also biases 'the Washer 33 and the adjusting member l21 carried thereby in a forward direction, thatis to say, toward the left as viewed in FIG. 2. This spring tension upon adjusting member 21 presses the tapering innerv 'portion 4t) of head piece 23 against the tapered surface 14 of bushing 11 and thus provides some amount of frictional binding force upon head piece .23, effecting afiner adjustment in the turning of said head piece, and also tending to eliminate back-lash in the setting of adjusting member 21. Thus, spring tension upon adjusting member 21 permits smooth, uniform, fine' adjustment of pistonelectrode 18 and-maintainsa'djusting member 21 in an exact adjusted position even when subjected to jarring,vibration,orthe like. The'engaging tapered surfaces' 14 and 40 alsoy provide good electrical Contact between the bushing 11 and adjusti-ng member 21.

` Akeyhole-likefslot 42 is provided in the threaded end portion-22 of shank 39,'the slot 42 permitting a slightv vdeformation inthe length of said threaded end portion"l 22. v The end of the threaded end portion 22 is slightly spaced from-the facing end of the square post 31 to per- I mit spring 30toexert a biasing force on the adjusting member 21.j Under tension of spring 30, the sections of the threaded-shank portion 22 are pressed together, bringing the external threading slightlyv out of alignmentV with the meshing vinternal threading 41 of piston electrode 19,

and thereby creating adrag on this screw threading'. This` tensioned drag serves to provide fine adjusting movement of the pistonelectrode`19, and also holds the latter in precise adjusted position'at all times, also eliminating back-lash and creepage.

The head member 23 is provided with a kerf 35 at the outer end thereof for the reception of a screw driver'or similar bladedtoolwhich may-be used to facilitate'the v rotationthereofduring adjustment.

The piston 19, front end. bushing 11, and adjusting member 21are made of a conductive metal which has Van extremely low coefficient ofthermal expansion. A

metallic, or electrically conductive ring 25, whichbears a terminal post 36 is placed around the front endV of cylinder 17 and is aflixed thereto in abutment with bushing 11.

Thus, terminal'post Sois electrically` connected to brush'- Ring 37 and integral terminal post 38, which are ideni tical to the aforementioned ring 25 and post 36, are sef cu'redto the band 24 of cylinder 17 bysoldering.

' As was previously' indicated, the metallic band 24 con;

' stitutes the ,fixed electrodeof the capacitor 10;V The band 24 and piston 18are separatedby the body 'of cylinder 17 which has a high dielectric constant.l Y The capacitance .of the units changedl by rotating adjusting screw 21,

this rotation being translated into longitudinal movement of piston 1S relative to fixed band 24. The piston 18 receives its charge through terminal 36, ring 25, bushing 11 and adjusting member 21. p

In the position of the capacitor shown in FIG. 2, the piston 19 is inrregistry with thel fixed electrode bandV 24,

f constituting the position of maximum capacitance. When the shank 39 is rotatedlby manual turning of the headV 23, the'piston 19 travels in Aa right-hand direction. (as viewedy in FIG. 2) away from the band 24 and the area of registry of the electrodes gradually decreases until the forward edge of the piston 19 `reaches the rearward (or right-hand) edge of the band 24, constitutingthe positionV of minimum capacitance. To permit suchposition to be reached, the washer Ztl is cupped or depressed at its center, as indicated at 2012 in FIG. 2, this depressed central,

area providingpclearance about the shank threaded end portion V22 when the piston approaches itspositionof vminimum capacitance. Y

Thus, it is seen from the above descriptionythe only pieces `of `capacitor 1@ which require extensive machining are the threaded portion 22 and internally threaded Y member 19. The complete unit is easily assembled with a minimum of cementing'and soldering.v Thus, production costs and assembling costs are considerably decreased and the capacitor is' capable of being more economically manufactured than lwasheretofore feasible. l

While a preferred embodimentof the invention has been shown and described herein, Vit is ,obviousv that numerousv changes, additions and omissions may be made in such embodiment without departing from the spiritand 'I scope of the invention.

What I claim isi n Y v y K.-

l.` A trimmer capacitor comprising al hollow cylinder formed of a material having a yhigh dielectric-constant, a bushing frictionally interttingwith and closing olf one end of said Ycylinden'said bushing having a through aper` yture communicating with the interiorfof saidV cylinder,

a rotatable'adjusting mem-ber'having a head located outside said bushing 'and a shank carried by said head and extending rotatably through said bushing intothe interior said noncircular aperture andvpreventing rotation of said piston electrode'within said cylinder.v wherebysaidfp'iston electrodefis moved longitudinally through said cylinder when theshank is rotated, the threaded terminal porY tion of said bore having a'transverse slotthereim'the free end of Asaid post engaging the'free end of said threadedy terminal portion, andv a spring between said,

bushing and said shank `urging the latter into firm engagement-with saidV post whereby said slot is compressed by said vpost to deform the threading on said 'terminalportion andcreate a tensioned drag on said piston elec' trode for `facilitating fine adjustment thereof.

l2. A trimmer `capacitor according to claim 1 in which said bushing has a tapered forward surface and saidrshanlr head has a corresponding tapered surface having a iiush engagement therewith, said spring urging said shank in an inward directionjandpressing the shank head ltaperedV l surface against the tapered forward surface of said bushing. l

a 'bushing frictionally interiitting with and closing Aoi'one end of V'said cylinder, said bus-hing having athro'ughaperture communicating with the` interior" of `said cylinder,"l l

3. A trimmer capacitorcomprising a hollow cylinder' i formed of a material having a khigh dielectric'constant,

rotatable adjusting member having a head located outside said bushing, a shank carried by said head and extending rotatably through said bushing into the interior of said cylinder, an externally-threaded terminal portion at the end of said shank, a cylindrical piston electrode slidable in said cylinder and having an internally-threaded bore receiving the threaded terminal portion of said shank, said piston carrying a member having a non-circular aperture in communication With said threaded bore, and an end cap secured to the end of said cylinder opposite said bore and having a longitudinally-extending post of non-circular cross-section, said post tting slidably Within said non-circular aperture and preventing rotation of said piston electrode within said cylinder whereby said piston electrode is moved longitudinally through said cylinder when the shank is rotated, the threaded terminal portion of said bore having a transverse slot therein, the free end of said post engaging the free end of said threaded terminal portion, said shank having a rectangular intermediate portion, a rst Washer having a rectangular groove making a snap-tit with said intermediate References Cited in the file of this patent UNITED STATES PATENTS 2,607,826 Barnes Aug. 19, 1952 2,747,147 Shull May 22, 1956 3,071,716 Young Jan. l, 1963 3,100,856 Barnes Aug. 13, 1963 FOREIGN PATENTS 263,948 Great Britain I an. l0, 1927 743,842 Germany Jan. 4, 1944 

1. A TRIMMER CAPACITOR COMPRISING A HOLLOW CYLINDER FORMED OF A MATERIAL HAVING A HIGH DIELECTRIC CONSTANT, A BUSHING FRICTIONALLY INTERFITTING WITH AND CLOSING OFF ONE END OF SAID CYLINDER, SAID BUSHING HAVING A THROUGH APERTURE COMMUNICATING WITH THE INTERIOR OF SAID CYLINDER, A ROTATABLE ADJUSTING MEMBER HAVING A HEAD LOCATED OUTSIDE SAID BUSHING AND A SHANK CARRIED BY SAID HEAD AND EXTENDING ROTATABLY THROUGH SAID BUSHING INTO THE INTERIOR OF SAID CYLINDER, AN EXTERNALLY-THREADED TERMINAL PORTION AT THE END OF SAID SHANK, A CYLINDRICAL PISTON ELECTRODE SLIDABLE IN SAID CYLINDER AND HAVING AN INTERNALLY-THREADED BORE RECEIVING THE THREADED TERMINAL PORTION OF SAID SHANK, SAID PISTON CARRYING A MEMBER HAVING A NON-CIRCULAR APERTURE IN COMMUNICATION WITH SAID THREADED BORE, AND AN END CAP SECURED TO THE END OF SAID CYLINDER OPPOSITE SAID BORE AND HAVING A LONGITUDINALLY-EXTENDING POST OF NON-CIRCULAR CROSS-SECTION, SAID POST FITTING SLIDABLY WITHIN SAID NON-CIRCULAR APERTURE AND PREVENTING ROTATION OF SAID PISTON ELECTRODE WITHIN SAID CYLINDER WHEREBY SAID PISTON ELECTRODE IS MOVED LONGITUDINALLY THROUGH SAID CYLINDER WHEN THE SHANK IS ROTATED, THE THREADED TERMINAL PORTION OF SAID BORE HAVING A TRANSVERSE SLOT THEREIN, THE FREE END OF SAID POST ENGAGING THE FREE END OF SAID THREADED TERMINAL PORTION, AND A SPRING BETWEEN SAID BUSHING AND SAID SHANK URGING THE LATTER INTO FIRM ENGAGEMENT WITH SAID POST WHEREBY SAID SLOT IS COMPRESSED BY SAID POST TO DEFORM THE THREADING ON SAID TERMINAL PORTION AND CREATE A TENSIONED DRAG ON SAID PISTON ELECTRODE FOR FACILITATING FINE ADJUSTMENT THEREOF. 